CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (AOCI) - Change in Each Component of AOCI (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Change in accumulated other comprehensive income (loss)
Balance, beginning of period			$ 193,946
Balance, end of period	$ 194,595	$ 197,070	194,595	$ 197,070
Net unrealized gains (losses) on debt securities
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	3,700	(412)	(265)	(2,250)
Other comprehensive income before reclassifications	(72)	566	4,735	2,842
Increase (decrease) due to amounts reclassified from AOCI	(210)	(259)	(1,052)	(697)
Total other comprehensive income	(282)	307	3,683	2,145
Balance, end of period	3,418	(105)	3,418	(105)
Debt valuation adjustment (DVA)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(36)	(376)	(944)	192
Other comprehensive income before reclassifications	(313)	215	599	(374)
Increase (decrease) due to amounts reclassified from AOCI	6	(5)	2	16
Total other comprehensive income	(307)	210	601	(358)
Balance, end of period	(343)	(166)	(343)	(166)
Cash flow hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	2,094	75	123	(728)
Other comprehensive income before reclassifications	(41)	172	2,083	772
Increase (decrease) due to amounts reclassified from AOCI	(194)	81	(347)	284
Total other comprehensive income	(235)	253	1,736	1,056
Balance, end of period	1,859	328	1,859	328
Benefit plans
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(7,172)	(6,574)	(6,809)	(6,257)
Other comprehensive income before reclassifications	189	(300)	(287)	(715)
Increase (decrease) due to amounts reclassified from AOCI	57	50	170	148
Total other comprehensive income	246	(250)	(117)	(567)
Balance, end of period	(6,926)	(6,824)	(6,926)	(6,824)
Foreign currency translation adjustment (CTA), net of hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(31,939)	(27,921)	(28,391)	(28,070)
Other comprehensive income before reclassifications	897	(1,442)	(2,651)	(1,293)
Increase (decrease) due to amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income	897	(1,442)	(2,651)	(1,293)
Balance, end of period	(31,042)	(29,363)	(31,042)	(29,363)
Excluded component of fair value hedges
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	8	5	(32)	(57)
Other comprehensive income before reclassifications	(39)	(10)	1	52
Increase (decrease) due to amounts reclassified from AOCI	0	0	0	0
Total other comprehensive income	(39)	(10)	1	52
Balance, end of period	(31)	(5)	(31)	(5)
Accumulated other comprehensive income (loss)
Change in accumulated other comprehensive income (loss)
Balance, beginning of period	(33,345)	(35,203)	(36,318)	(37,170)
Other comprehensive income before reclassifications	621	(799)	4,480	1,284
Increase (decrease) due to amounts reclassified from AOCI	(341)	(133)	(1,227)	(249)
Total other comprehensive income	280	(932)	3,253	1,035
Balance, end of period	$ (33,065)	$ (36,135)	$ (33,065)	$ (36,135)